The present invention relates to an AFC circuit, a carrier recovery circuit and a receiver for use in satellite digital television broadcasting and more particularly to an AFC circuit, a carrier recovery circuit and a receiver for regenerating a carrier even at the time of low C/N ratio.
For digital transmission through a satellite, hierarchical transmission method capable of data transmission to some extent even at the time of a low C/N ratio by adaptive transmission by time division based on modulation method having different numbers of constellation points by considering a deterioration of the C/N ratio due to rain attenuation or the like has been invented. In such a transmission method, it is very difficult to obtain a reference signal necessary for carrier recovery from a period of modulation wave having many constellation points at the time of low C/N ratio, and therefore, a carrier recovery method which is an ordinary carrier recovery method for continuously regenerating the carrier, cannot be used.
Accordingly, an object of the present invention is to achieve carrier recovery by disposing periodically a modulated signal period with few constellation points which is modulated by, for example, BPSK modulation method or QPSK modulation method and from which a reference carrier signal having a considerable CN rate can be obtained, and fetching out phase/frequency error information periodically. Further, because, according to a method for observing a phase error signal periodically, with a frequency of a predetermined period, the same phase error signal is obtained, so-called false lock phenomenon in which the frequency is apparently synchronized with a different frequency from its proper carrier frequency occurs. To avoid this phenomenon, a modulated signal with few constellation points which is modulated by, for example, BPSK modulation method or QPSK modulation method is set at a predetermined interval and in the pseudo synchronizing state, a frequency of a difference from the proper carrier frequency is observed by using such a fact that the reception signal phase is rotated in a predetermined direction so as to control the VCO (Voltage Controlled Oscillator) thereby making it possible to synchronize with the proper frequency. In the modulation period having few constellation points, detection of the pseudo synchronizing state and synchronization with a desired frequency are enabled using a statistical characteristic of an observed signal.
In a conventional transmission method of transmitting a modulated signal having many constellation points continuously or a method in which the number of constellation points is changed by time division system, if carrier recovery is carried out continuously, when the C/N ratio drops, a stabilized carrier recovery signal cannot be obtained in a modulation period having many constellation points. For this reason, even if a modulated signal having few constellation points exists, stable demodulation is disabled.
Further, in a method for carrying out carrier recovery periodically using only a period having a few constellation points for such a modulated signal, there is a problem that false lock occurs by observing the phase periodically. Therefore, a wide capture range cannot be achieved. Thus, because a very high frequency stabilization accuracy is demanded in the transmission system containing the frequency conversion portion, the receiver device becomes very expensive.
For the reason, according to the method for transmitting modulated signals having different numbers of constellation points in time division system, if the conventional carrier recovery system is utilized, the carrier recovery is disabled when the C/N ratio is low.
Then, although a method for controlling the VCO or NCO (Numerical Controlled Oscillator) can be considered by measuring the phase with only a period having a few constellation points, there is a problem that a wide capture range cannot be achieved because of false lock phenomenon caused by observing the phase periodically.
The present invention has been achieved in viewpoints of the above problems and therefore it is an object of the invention to provide an AFC circuit capable of regenerating a carrier signal synchronous with the inputted signal in terms of the frequency while preventing an occurrence of false lock even when a reference signal period or a modulated signal period having a few constellation points which can be used for carrier recovery, contained in an input signal, is short or even when noise is mixed in the inputted signal.
Another object of the invention is to provide a carrier recovery circuit capable of regenerating the carrier signal stably in a wide capture range by transmitting modulations signal having different numbers of constellation points by time-division system and carrying out carrier synchronization using phase and frequency error information obtained periodically even if the C/N ratio is low when a modulated signal is received and regenerated.
Still another object of the invention is to provide a receiver device capable of regenerating information contained in digitally modulated signal by carrying out carrier synchronization using phase and frequency error information obtained periodically and regenerating the carrier signal stably in a wide capture range even if the C/N ratio is low when digitally modulated signal provided with a reference signal period or digitally modulated signal period having a few constellation points to be useful for carrier recovery at a predetermined time interval is received and regenerated.
To achieve the above object, the AFC circuit for detecting a frequency difference between two inputted signals and zeroing said frequency difference between the inputted signals according to the detection result, comprises: a frequency difference detecting portion for detecting a phase difference between the inputted signals and generating a frequency correction signal according to the phase difference or a time differential value of the phase difference; and a frequency difference correcting portion for rotating the phase of the inputted signal according to the frequency correction signal outputted from the frequency difference detecting portion so as to zero the frequency difference between the inputted signals.
In the AFC circuit for detecting a frequency difference between two inputted signals and zeroing the frequency difference between the inputted signals according to the detection result, a frequency difference detecting portion detects a phase difference between the inputted signals and generates a frequency correction signal according to the phase difference or a time differential value of the phase difference and a frequency difference correcting portion rotates phase of the inputted signals according to the frequency correction signal outputted from the frequency difference detecting portion so as to zero the frequency difference between the inputted signals. As a result, even when the reference signal period modulated signal period having few constellation points which is usable for regenerating a carrier contained in the inputted signals is short or even when noise is mixed in the inputted signals, a carrier signal synchronous with the inputted signals is regenerated while preventing an occurrence of false lock.
Another feature of the invention is an AFC circuit for detecting a frequency difference between two inputted signals and zeroing said frequency difference between the inputted signals according to the detection result, the AFC circuit comprising: a correlation computing portion for detecting a phase difference between the inputted signals and computing an autocorrelation coefficient of the phase difference; and a frequency difference correcting portion for counting a number of peaks in a waveform of the autocorrelation coefficient obtained by the correlation computing portion and rotating phase of the inputted signals according to the count result so as to zero the frequency difference between the inputted signals.
In the AFC circuit in the preceding paragraph for detecting a frequency difference between two inputted signals and zeroing the frequency difference between the inputted signals according to the detection result, a correlation computing portion detects a phase difference between the inputted signals and computes an autocorrelation coefficient of the phase difference and a frequency difference correcting portion counts the number of peaks in a waveform of the autocorrelation coefficient obtained by the correlation computing portion and rotates phase of the inputted signals according to the count result so as to zero the frequency difference between the inputted signals. As a result, even when the reference signal period or modulated signal period having few constellation points which is usable for regenerating a carrier contained in the inputted signal is short or even when noise is mixed in the inputted signal, a carrier signal synchronous with the inputted signal is regenerated while preventing an occurrence of false lock.
Another feature of the invention is an AFC circuit for detecting a frequency difference between two inputted signals and zeroing said frequency difference between the inputted signals according to the detection result, the AFC circuit comprising: a correlation computing portion for detecting a phase difference between the inputted signals and computing an autocorrelation coefficient of a waveform varying in time of the phase difference; and a frequency difference correcting portion for obtaining an average period of a periodic waveform appearing in a waveform of the autocorrelation coefficient obtained by the correlation computing portion and rotating a phase between the inputted signals according to the average period so as to zero the frequency difference of the inputted signals.
In the last described AFC circuit for detecting a frequency difference between two inputted signals and zeroing the frequency difference between the inputted signals according to the detection result, a correlation computing portion detects a phase difference between the inputted signals and computes an autocorrelation coefficient of a waveform varying in time of the phase difference and a frequency difference correcting portion obtains an average period of periodic waveform appearing in a waveform in the autocorrelation coefficient obtained by the correlation computing portion and rotates a phase between the inputted signals according to the average period so as to zero the frequency difference of the inputted signals. As a result, even when the reference signal period or modulated signal period having few constellation points which is usable for regenerating a carrier contained in the inputted signal is short or even when noise is mixed in the inputted signal, a carrier signal synchronous with the inputted signal is regenerated while preventing an occurrence of false lock.
A further feature of the present invention is an AFC circuit for detecting a frequency difference between two inputted signals and zeroing said frequency difference between the inputted signals according to the detection result, the AFC circuit comprising: a region determining portion for detecting a phase difference between the inputted signals and determining which region each signal point is included in according to the phase difference; and a frequency difference correcting portion for counting a determination result of the region determining portion for each phase and for each determining region rotated at a rotation speed corresponding to a set frequency, and rotating phase of the inputted signals according to the count result so as to zero the frequency difference between the inputted signals.
In the last described AFC circuit for detecting a frequency difference between two inputted signals and zeroing the frequency difference between the inputted signals according to the detection result, a region determining portion detects a phase difference between the inputted signals and determines which region each signal point is included in according to the phase difference and a frequency difference correcting portion counts a determination result of the region determining portion for each phase and for each determining region rotated at a rotation speed corresponding to a set frequency and rotates phase of the inputted signals according to the count result so as to zero the frequency difference between the inputted signals. As a result, even when the synchronization period for the inputted signal is short or even when noise is mixed in the inputted signal, a carrier signal synchronous with the inputted signal is regenerated while preventing an occurrence of false lock.
A further feature of the invention is a carrier recovery circuit for regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, the circuit comprising: a frequency difference detecting portion for detecting a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal, and generating a frequency correction signal according to the phase difference or a differential value of the phase difference; and a frequency difference correcting portion for controlling a frequency of the regeneration carrier signal according to the frequency correction signal outputted from the frequency difference detecting portion so as to zero a frequency difference between the reception signal and the regeneration carrier signal.
In the carrier recovery circuit for regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, a frequency difference detecting portion detects a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal and generates a frequency correction signal according to the phase difference or a differential value of the phase difference and a frequency difference correcting portion controls a frequency of the regenerated carrier signal according to the frequency correction signal outputted from the frequency difference detecting portion so as to zero a frequency difference between the reception signal and the regenerated carrier signal. As a result, upon transmitting a modulated signal having different numbers of constellation points by time division system and receiving the signal, even when the C/N ratio is low, the carrier synchronization is carried out using information of the phase and frequency obtained periodically, so that the carrier signal is regenerated stably in a wide capture range.
Yet another feature of the invention is a carrier recovery circuit regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, the circuit comprising: a correlation computing portion for detecting a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal so as to compute autocorrelation coefficients of the phase difference; and a frequency difference correcting portion for counting peaks of the waveform of the autocorrelation coefficient waveform obtained by the correlation computing portion and controlling a frequency of the regenerated carrier signal according to the count result so as to zero the frequency difference between the reception signal and the regenerated carrier signal.
In the last described carrier recovery circuit for regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, a correlation computing portion detects a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal so as to compute autocorrelation coefficients of the phase difference and a frequency difference correcting portion counts peaks of a waveform of the autocorrelation coefficient obtained by the correlation computing portion and controls frequency of the regeneration carrier signal according to the result so as to zero the frequency difference between the reception signal and the regenerated carrier signal. As a result, upon transmitting a modulated signal having different numbers of constellation points by time division system and receiving the signal, even when the C/N ratio is low, the carrier synchronization is carried out using information of the phase and frequency obtained periodically, so that the carrier signal is regenerated stably in a wide capture range.
A further feature of the invention is a carrier recovery circuit for regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, the circuit comprising: a correlation computing portion for detecting a phase difference between the regenerated carrier signal and the reception signal from the I baseband signal and the Q baseband signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal so as to compute autocorrelation coefficients of the phase difference; and a frequency difference correcting portion for obtaining an average period of a periodic waveform appearing in a waveform of the autocorrelation coefficient obtained by the correlation computing portion, and controlling a frequency of the regenerated carrier signal based on the average period so as to zero the frequency difference between the reception signal and the regenerated carrier signal.
In the last described carrier recovery circuit for regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, a correlation computing portion detects a phase difference between the regenerated carrier signal and the reception signal from the I baseband signal and the Q baseband signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal so as to compute the autocorrelation coefficients of the phase difference. A frequency difference correcting portion obtains an average period of a periodic waveform appearing in a waveform of the autocorrelation coefficient obtained by the correlation computing portion and controls frequency of the regenerated carrier signal based on the average period so as to zero the frequency difference between the reception signal and the regenerated carrier signal. As a result, upon transmitting a modulated signal having different numbers of constellation points by time division system and receiving the signal, even when the C/N ratio is low, the carrier synchronization is carried out using information of the phase and frequency obtained periodically, so that the carrier signal is regenerated stably in a wide capture range.
Another feature of the invention is a carrier recovery circuit for regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, the circuit comprising: a region determining portion for detecting a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal, and determining which region of a phase plane each signal point is included in based on the phase difference; and a frequency difference/phase difference correcting portion for counting a determination result of the region determining portion for each phase and for each determination region rotated at a rotation speed corresponding to a set frequency, and controlling frequency and phase of the regenerated carrier signal based on the count result so as to zero a frequency difference and the phase difference between the reception signal and the regenerated carrier signal.
In the last described carrier recovery circuit for regenerating a carrier signal from an I baseband signal and a Q baseband signal obtained by quadrature-demodulating a reception signal, a region determining portion detects a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal and determine which region of a phase plane each signal point is included in based on the phase difference and a frequency difference correcting portion counts a determination result of the region determining portion for each phase and for each determination region rotated at a rotation speed corresponding to a set frequency and controls frequency and phase of the regenerated carrier signal based on the count result so as to zero the frequency difference and phase difference between the reception signal and regenerated carrier signal. As a result, upon transmitting a modulated signal having different numbers of constellation points by time division system and receiving the signal, even when the C/N ratio is low, the carrier synchronization is carried out using information of the phase and frequency obtained periodically, so that the carrier signal is regenerated stably in a wide capture range.
Another feature of the invention is a receiver device for regenerating a carrier signal based on the I baseband signal and the Q baseband signal obtained by quadrature-demodulating a reception signal, and decoding the I baseband signal and the Q baseband signal so as to regenerate information, said receiver device further receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having few constellation points to be used for carrier recovery at a predetermined time interval; and establishing carrier synchronization using information about phase error and frequency error obtained in the reference signal period or in the digitally modulated signal period having constellation points.
In the last described receiver device for regenerating a carrier signal based on the I baseband signal and the Q baseband signal obtained by quadrature-demodulating a reception signal, and decoding the I baseband signal and the Q baseband signal so as to regenerate information, the receiver device further receives a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having few constellation points to be used for carrier recovery at a predetermined time interval and establishes carrier synchronization using information about phase error and frequency error obtained in the reference signal period of the digitally modulated signal or the digitally modulated signal period. As a result, upon receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having a few constellation points useful for carrier recovery at a predetermined time interval, even when the C/N ratio is low, carrier synchronization is carried out using phase and frequency error information obtained periodically and then a carrier signal is regenerated stably in a wide capture range so as to regenerate information contained in digitally modulated signal.
The receiver device for regenerating a carrier signal based on the I baseband signal and the Q baseband signal obtained by quadrature-demodulating a reception signal, and decoding the I baseband signal and the Q baseband signal so as to regenerate information, further receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having few constellation points to be used for carrier recovery at a predetermined time interval; and detecting a difference between a regeneration carrier frequency and a carrier frequency of the reception signal obtained in a reference signal period or in a digitally modulated signal period having few constellation points so as to achieve at least one of AFC function or false lock preventing function based on the detection result.
In the receiver device for regenerating a carrier signal based on the I baseband signal and the Q baseband signal obtained by quadrature-demodulating a reception signal, and decoding the I baseband signal and the Q baseband signal so as to regenerate information, the receiver device further receives a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having few constellation points to be used for carrier recovery at a predetermined time interval and detecting a difference between the regenerated carrier frequency and the carrier frequency of the reception signal obtained in a reference signal period of the digitally modulated signal or a digitally modulated signal period so as to achieve at least one of AFC function or false lock preventing function based on the detection result. As a result, upon receiving a digitally modulated signal provided with a reference signal period or with a digitally modulated signal period having a few constellation points useful for carrier recovery at a predetermined time interval, even when the C/N ratio is low, carrier synchronization is carried out using phase and frequency error information obtained periodically and then a carrier signal is regenerated stably in a wide capture range so as to regenerate information contained in digitally modulated signal.
The receiver device last described includes a regeneration carrier frequency controlled according to detuning frequency information obtained by time differential value or a primary inclination of a change of a phase obtained by observing a phase variation in a reference signal period of a reception signal or in a modulated signal period having few constellation points, under a state of frequency asynchronization.
The regeneration carrier frequency is controlled according to detuning frequency information obtained by time differential value or a primary inclination of a change of a phase obtained by observing a phase variation in a reference signal period of a reception signal or in a modulated signal period having few constellation points, under a state of frequency asynchronization. As a result, upon receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having a few constellation points useful for carrier recovery at a predetermined time interval, even when the C/N ratio is low, carrier synchronization is carried out using phase and frequency error information obtained periodically and then a carrier signal is regenerated stably in a wide capture range so as to regenerate information contained in digitally modulated signal.
In the receiver device of the present invention a detuning frequency is estimated based on periodicity of an autocorrelation coefficient waveform in a phase variation curve obtained by observing a phase variation in a reference signal period of a reception signal or in a modulated signal period having few constellation points and then a regeneration carrier frequency is controlled based on detuning frequency information obtained by the estimation operation, under a state of frequency asynchronization.
In the receiver device a detuning frequency is estimated based on periodicity of an autocorrelation coefficient waveform in a phase variation curve obtained by observing a phase variation in a reference signal period of a reception signal or a modulated signal period having few constellation points and then a regeneration carrier frequency is controlled based on detuning frequency information obtained by the estimation operation. As a result, upon receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having a few constellation points useful for carrier recovery at a predetermined time interval, even when the C/N ratio is low, carrier synchronization is carried out using phase and frequency error information obtained periodically and then a carrier signal is regenerated stably in a wide capture range so as to regenerate information contained in digitally modulated signal.
In the receiver device the regeneration carrier frequency is set at a low frequency preliminarily so as to provide a frequency of a waveform or a number of correlation peaks appearing in the autocorrelation coefficient waveform relative to a desired frequency with an offset, thereby making it possible to estimate a detuning frequency lower than the desired frequency.
Further, in the receiver device, the regeneration carrier frequency is set at a low frequency preliminarily so as to provide a frequency of a waveform or the number of correlation peaks appearing in an autocorrelation coefficient waveform relative to a desired frequency with an offset, thereby making it possible to estimate a detuning frequency lower than a desired frequency. As a result, upon receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having a few constellation points useful for carrier recovery at a predetermined time interval, even when the C/N ratio is low, carrier synchronization is carried out using phase and frequency error information obtained periodically and then a carrier signal is regenerated stably in a wide capture range so as to regenerate information contained in digitally modulated signal.
In accord with the present invention, the receiver device is a receiver device wherein whether or not carrier synchronization is established is detected based on a statistical characteristic of phase points of a signal in a modulation period having few constellation points and oscillation frequency sweep of a local oscillator for use for frequency conversion is stopped based on the detection result.
In the receiver device of the preceding paragraph whether or not carrier synchronization is established is detected based on a statistical characteristic of phase point of a signal in a modulation period having few constellation points and oscillation frequency sweep of a local oscillator for use for frequency conversion is stopped based on the detection result. As a result, upon receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having a few constellation points useful for carrier recovery at a predetermined time interval, even when the C/N ratio is low, carrier synchronization is carried out using phase and frequency error information obtained periodically and then a carrier signal is regenerated stably in a wide capture range so as to regenerate information contained in digitally modulated signal.
The receiver device of the present invention is a receiver device for regenerating a carrier signal based on the I baseband signal and the Q baseband signal obtained by quadrature-demodulating a reception signal, and decoding the I baseband signal and the Q baseband signal so as to regenerate information, said receiver device further including a carrier recovery circuit comprising: a receiving portion for receiving a digitally modulated signal provided with a reference signal period or with a digital modulation period having few constellation points to be used for carrier recovery at a predetermined time interval so as to obtain the reception signal; a region determining portion for detecting a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal, and determining which region of a phase plane each signal point is included in based on the phase difference; and a frequency difference/phase difference correcting portion for counting a determination result of the region determining portion for each phase and for each determination region rotated at a rotation speed corresponding to a set frequency, and controlling frequency and phase of the regenerated carrier signal based on the count result so as to zero a frequency difference and the phase difference between the reception signal and the regenerated carrier signal, whereby at least one of AFC function or false lock preventing function being achieved.
In the receiver device for regenerating a carrier signal based on the I baseband signal and the Q baseband signal obtained by quadrature-demodulating a reception signal, and decoding the I baseband signal and the Q baseband signal so as to regenerate information, the receiver device further includes a carrier recovery circuit comprising a receiving portion for receiving a digitally modulated signal provided with a reference signal period or with a digital modulation period having few constellation points to be used for carrier recovery at a predetermined time interval, a region determining portion for detecting a phase difference between the regenerated carrier signal and the reception signal from the I axis side signal and the Q axis side signal obtained by quadrature-demodulating the reception signal by the regenerated carrier signal and determining which region of a phase plane each signal point is included in based on the phase difference, a frequency difference/phase difference correcting portion for counting a determination result of the region determining portion for each phase and for each determination region rotated at a rotation speed corresponding to a set frequency, and controlling frequency and phase of the regeneration carrier signal based on the count result so as to zero the frequency difference and phase difference between the reception signal and regenerated carrier signal, whereby at least one of AFC function or false lock preventing function being achieved. As a result, upon receiving a digitally modulated signal provided with a reference signal period or a digitally modulated signal period having a few constellation points useful for carrier recovery at a predetermined time interval, even when the C/N ratio is low, carrier synchronization is carried out using phase and frequency error information obtained periodically and then a carrier signal is regenerated stably in a wide capture range so as to regenerate information contained in digitally modulated signal.